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Reliable delivery of concrete in large projects

A precise dance of booms and cranes at “The Circle” in Zurich

June 2018 | Europe | Story

Directly in front of Zurich Airport, Flughafen Zürich AG and Swiss Life are investing a billion Swiss francs into the new business district “The Circle”. Architect Riken Yamamoto designed this new commercial centre as a connecting element between the airport and the park behind it. The side of the structure facing the street will have a largely closed, curved façade. On the park side, however, the building will be more airy and open up towards the green space.

Three construction companies, Barizzi, Anliker and Frutiger, are involved in what is currently the largest building project in Switzerland. The concreting works for all three companies are carried out by a3 Betonpumpen AG from Affoltern am Albis. Construction on the building carcass is expected to be complete by 2019, the grand opening is planned for mid-2020.

At the beginning, everything was still quite simple. There was sufficient space for transporting materials and equipment to and from the construction site. But the quick progress meant that the majority of the area was soon concreted, and only a few access points remained. All logistic elements of the construction site now had to be completed through a narrow drive. This hurdle could be overcome through coordinated project planning.

A quick glance at the surrounding area soon reveals that space around the construction site is in short supply as well, due to the airport and the connecting roads. The curved building now being constructed will elegantly project over the existing airport approach road. To ensure that no parts can fall on cars or pedestrians during the construction phase, a specially built, angled massive steel wall was installed in front of the building.

Another big challenge was posed by the existing SBB airport train, which runs only 4 m below the planned building foundation at some points. In order to avoid any problems with the train, the decision was made to use twice as many piles as originally planned, extending the construction phase by half a year.

Today, the construction site is dominated by many cranes and booms reaching up into the sky. Their number and position is precisely planned so that they do not impede each other. “We have reached our limit,” Gery Schär, Managing Director of a3 Betonpumpen AG, says. “The many placing booms and cranes need to be positioned precisely and with a great deal of caution so that everything works as intended.”

Before the start of the project, different concreting options were discussed. For reasons of space and capacity, the following solution was implemented. Six tubular columns, each with a stationary Putzmeister placing boom with a horizontal reach of 32 m (MX 32-4), were installed on compact cruciform bases across the construction site. Three stationary Putzmeister concrete pumps (BSA 2109 HD and 2109 HD4, and BSA 2110 HD), placed at different points of the site, supply them with concrete through different pipelines. One BSA concrete pump supplies one placing boom, the second BSA supplies two different booms and the third pump can supply another three booms with concrete. All MX placing booms are also fitted with EQV squeeze valves, which prevent concrete from dripping from the end hose when the booms are slewed. The communication between the BSA machine operator from a3 and the boom operator takes place via radio on particular frequencies, which are only used by the concreting crew on the construction site.

Different types of concrete in use

Using ZX and SK pipelines, various types of concrete are pumped over distances of up to 250 m. In some cases, the concrete is extremely stiff. Depending on which of the three mixing systems operated by Toggenburger, Eberhard or Kibag provides the concrete, broken or round material is used. For concreting the radiation-protection areas of the university hospital, high-density concrete was pumped and poured into the formwork through a shortened RV 10 rotary distributor.

Sophisticated cleaning

The type of cleaning used on the site was specially developed by a3 for this project. As early as the planning stage, it had become clear that the conventional cleaning method of cleaning the concrete pump first and then pumping water through the pipeline would take too long. To circumvent this problem, a3 placed a cleaning container with a 200 bar high-pressure water pump and a water container next to each BSA. Cleaning pipes with pigs and rolled-up cement bags are prepared by the concreting team and readily available next to the machine. After concreting, the first delivery line elbow behind the pressure connection is removed, the cleaning pipe connected and the concrete pushed out of the pipeline towards the stationary boom by the high-pressure water pump via a water hose. The concrete is mostly used for formwork, and the water pressed back from the boom to the water tank using compressed air.

Operation and maintenance by a3

All stationary Putzmeister concrete pumps are operated exclusively by the a3 team. The workshop personnel and service engineers stationed on-site ensure that all machines are in a good operating state. As Schär says: “Considering that we pump tens of thousands of cubic metres of concrete in a very short time, that is the only way to ensure everything runs smoothly.” He adds: “I regularly visit the construction site to get feedback and provide support. We buy spare parts directly from Robert Aebi AG, our reliable partner for all things Putzmeister.”

Around 20–600 m³ of concrete are pumped each day. During the entire construction phase, that will add up to a total of approx.170,000 m³ of concrete. Another two years will go by until what will become Switzerland's longest building with its 800 m long curved façade is complete. At that point, a gross floor area of 180,000 m2will be available on a base area of 30,000 m2, which will be used for a hotel, shopping outlets and offices, as well as the University Hospital Zurich.

Gery Schär (2nd from right), Managing Director of a3 Betonpumpen, explains concreting logistics. a3 Betonpumpen was awarded the project thanks to the company's high level of expertise and the available fleet of machines